Cook the colocasia tubers in boiling water till the tubers become smooth. Peel the outer husk and keep the tubers aside.
Add warm water to the tamarind, soak for about fifteen minutes and extract thick juice into a bowl.
Take a deep bottomed pan, add oil and heat. Splutter the mustard seeds.
Add the onion pieces and fry until brown. Add the tomato pieces, ginger-garlic paste, green chilly pieces, turmeric powder, red chilly powder and roughly mashed garlic bulbs and simmer until tomato pieces become smooth.
Add the colocasia tubers, coriander seed powder, curry leaves and enough salt. Mix well and fry till oil shows up.
Add the tamarind juice and jaggary, mix thoroughly, add water and place a lid on the pan.
Allow the contents to simmer in medium flame till cooked well.
Top the dish with chopped coriander leaves and serve hot with rice.